There is a very strange thing: It works iconifying with RTG or AfAOS with AmiKit.

So I've tried:

Using the AmiKit WinUAE configuration with CWB39 or AKReal
Using the S-S and User-Startup of AmiKit
Installing again AISS and MUI5 over AmiKit
Disabling the WBStartup
Changing AKReal to use UAEgfx instead of Picasso.